1. Field of the Invention
This invention relates to a fluid friction coupling having at least two sets of plates, the coupling comprising a first coupling part in the form of a hub and a second coupling part in the form of a housing which is at least partially filled with a viscous fluid, one of the sets of plates being non-rotatably connected to the first coupling part and the other set of plates being non-rotatably connected to the second coupling part, the plates of the two sets of plates being arranged to alternate and to radially overlap one another.
2. Description of Prior Art
There are prior art fluid friction couplings operating with slotted plates which are provided with scraping edges at the slot rims in the form of thickened portions (see West German Patent Specification No. 36 32 283). These improve the transition from the normal operating mode of the coupling to the hump mode. The term "hump mode" is known to those skilled in the art and is used to describe the condition where the plates are in frictional contact with each other. The scraping edge of the slot rims ensures that the fluid film is scraped off the plane face of the other plate in accordance with the operating principle of a windscreen wiper. However, the removed particles resulting from the friction contact cause a ball bearing effect which reduces the torque transmitting capacity.